Since the late 1980s, the micro-electromechanical system (MEMS) has gotten a lot of attention. MEMS is the general name for the integrated micro-elements and systems. Furthermore, MEMS includes the electrical and mechanical components manufactured by the batch processing technology applying the integrated circuit (IC) compatibility. In addition, the sizes of the manufactured components are ranged from micrometers to millimeters.
Since MEMS has the properties, such as compact volumes, powerful functions and low costs, etc., various industries including semiconductor industry, electronics industry, engineering industry, communication industry, bioindustry, and chemical industry have invested huge capitals in relevant researches. Accordingly, the relevant products, such as accelerators, optical communication switches and biosensors are presented to the public one by one.
Since the first ruby laser was presented in 1960s, other lasers, such as the gas laser and the semiconductor laser, are presented successively and rapidly developed. In which, the tunable lasers are widely applied in the science fields, such as the optical fiber communications, the optical data processing and the multi-wavelength interferences. The grating-feedback external cavity tunable laser is especially conspicuous because of its manifold advantages, such as the wide ranges of the tunable wavelengths, the narrow bandwidths of signals, low costs, simple operations and being driven easily.
Due to the keen competitions in the communication technologies, the optical fiber communications must be gradually changed from the recent long-distance telecommunication networks and cable television arterial networks to the short-distance local information networks and subscriber loops. Since the optical communication active elements and the simulation technologies are the determinants of the optical communication industries, various factories are devoted to improve the efficacies of the optical communication active elements. Further, due to the tunable laser is an essential component to the optical communication active elements, to find out the way of how to improve the tunable laser has become the topical subject.
The conventional grating-feedback external cavity tunable laser systems can be simply divided into three types, the Littrow type, the Grazing incident type, and the Fabry-Perot type. In which, the laser of the Littrow type has high diffraction efficiency but low resolution. The laser system of the Grazing incident type has higher resolution than that of the Littrow type because its incident beam is oblique to the grating. Further, the laser system of the Grazing incident type usually includes a reflector, a lens and an I-type plate or a V-type plate, so that it is possible to control the wavelength of the output light by fine adjusting the relevant angles between the components. Nevertheless, the structure of the laser system of the Grazing incident type is more complex than that of the Littrow type because it has the additional components of I-type plate or the V-type plate. In addition, the laser system of the Fabry-Perto type does not use the above design of gratings, it disperses the light by the resonance cavity composed of one side of a laser diode, which is the light source of the laser system and has the other side coated with a resist layer, and one side of a reflector located within the laser system. The wavelengths of the output light are controlled by changing the length of the resonance cavity. Although the laser system of the Fabry-Perto type can output the lights with multi-wavelengths, its cost and structure complexity is higher than those of the Littrow type and the Grazing incident type.
As above-mentioned description, since the laser system of the Grazing incident type has better resolution than that of the Littrow type and has simpler operating process than that of the Fabry-Perot type, the grating-feedback external cavity tunable laser, one kind of the laser systems of the grating tunable incident type, has become the main subjects of the relevant researches. However, in the conventional grating-feedback external cavity tunable laser, in order to control the wavelengths of the output lights, the components with the anti-dazzling efficiency, such as the foregoing I-type plate and the V-type plate, are necessary. But, the structure complexity of the grating-feedback external cavity tunable laser is increased due to the foregoing components. Therefore, the research subject of the grating-feedback external cavity tunable laser is to simplify the structure without affecting the function of controlling the wavelengths of the output lights.
However, as to the micro optical elements within the free space, the elements which are often used to make the reflective light reflect along the direction reverse to that of the incident light are micro mirrors, micro corner mirrors, and micro corner cube, or the combination thereofwhich are shown in FIGS. 1(A)-1(C) respectively.
Please refer to FIG. 1(A). As shown in FIG. 1(A), if the incident light is parallel to the normal of the micro mirror, the reflective light would feed back along the direction reverse to that of the incident light. However, in the actual applications, in order to make the reflective lights transmitted along the direction reverse to that of the incident light, some actuators are essential for adjusting the micro mirror.
Please refer to the FIG. 1(C), which is a schematic diagram of the micro corner cube according to the prior art. Based on the micro corner cube shown in FIG. 1(C), in theory, when a incident light incidences any mirror of the corner cube, its reflective light would be transmitted along the direction reverse to that of the incident light. Accordingly, when the light spot of laser has size similar to the opening size of the corner cube, the reflective light would be considered as a reverse light of the incident light, and that is to say the optical feedback is achieved. The three mirrors of the corner cube are separately manufactured by the buck micromachining technology of MEMS. However, since the three mirrors are combined with one another via fasteners, the perpendicularities between any two mirrors are not easily controlled.
Please refer to the FIG. 1(B), which is a schematic diagram of the micro corner mirror according to the prior art. As to the micro corner mirror shown in FIG. 1(B), in theory, when an incident light incidences one mirror of the corner mirror, its reflective light would be transmitted along the direction reverse to that of the incident light. Accordingly, when the light spot has the size similar to the opening size of the corner mirror, the reflective light would be considered as a reverse light of the incident light, and that is to say the optical feedback is achieved. Therefore, when one of the mirrors is rotated and the perpendicularity between the two mirrors is destroyed accordingly, the optical feedback would not be achieved. That is to say the optical feedback is selective. Further, with regard to a laser system having plural corner mirrors arranged therein, since the perpendicularities of the plural corner mirrors are able to be selectively destroyed, the wavelengths of the irradiative lights of the laser system are controllable.
Therefore, in order to reduce the complexity of the structures and increase the conveniences of selecting the wavelengths of the output lights, a new tunable laser system having the micro corner mirror array manufactured by MEMS technology is ably needed in the industry.
In addition, the general allowable error range of the perpendicularity standard for the present merchant corner mirror is ±0.08°, which is caused by the mechanical errors or artificial errors. However, the error range of ±0.08° is negligible for general optical elements, but it is enormous for MEMS elements. In other words, a new corner mirror type having more accurate perpendicularity is desirous. Thus, to improve the perpendicularity accuracy of the corner mirror is also a research subject for semiconductor laser system.
In the view of aforesaid discussion, how to built a laser system having better resolution, compacter structure, easier operating processes, tunable wavelengths of the output lights, and lower cost is an industrial subject at present.